1. Field of the Invention
The present invention relates to a functional film and an organic EL device. Specifically, the present invention relates to a functional film having excellent optical characteristics in addition to excellent functions such as a high gas barrier property, and to an organic EL device using the functional film.
2. Description of the Related Art
An organic EL device is a self-light emitting device, and is used in a display (a display device), an illumination device, and the like.
For example, an organic EL display has display performance advantages such as high visibility and excellent viewing angle characteristics compared to a CRT or a liquid crystal display of the related art.
In addition, an organic EL device is able to realize weight reduction and thickness reduction, and thus it is possible to enhance weight reduction or thickness reduction of the display or the illumination device.
Furthermore, the device is configured by using a substrate with flexibility, and thus it is possible to manufacture a device having flexibility. Accordingly, a flexible display is able to be realized, and an illumination device of a shape which has not been realized so far is able to be manufactured.
In the related art, an organic EL device in which a plastic film is used as a substrate (a plastic substrate) instead of a glass substrate being used is considered for flexibility, furthermore for weight reduction, or the like.
In general, an organic EL device is configured to be interposed between sealing glass and glass of the substrate. Here, when the plastic film is used on a light extraction side of the sealing glass instead of glass, a low retardation film (a low phase difference film) formed of a polycarbonate, a cyclo-olefin polymer, or the like is required in order to improve contrast of light or suppress external light reflection. In addition, in the organic EL device, when the low retardation film is used instead of the sealing glass, the low retardation film is required to have a gas barrier property similar to that of glass.
On the other hand, when the organic EL device sealed with glass is provided with a phase difference film or a polarization plate for external light control, the low retardation film may be used as a protective film. As the low retardation film, a gas barrier film in which a gas barrier property is conferred is used, and thus it is possible to prevent the low retardation film from being separated from the glass substrate or from being deformed due to expansion of a base material by external humidity or heat.
As the gas barrier film (a plastic film in which a high gas barrier property is conferred) having a high gas barrier property, a gas barrier film having a laminated structure of an organic layer and an inorganic layer is known as disclosed in JP2009-269193A. The gas barrier film has a configuration in which a plastic film such as a PET film or a PEN film is formed as a support body, an organic layer as a base layer is formed on a surface of the support body, and an inorganic layer such as silicon nitride exhibiting a gas barrier property is formed on the organic layer.
In the gas barrier film, the organic layer is formed as a base, and thus it is possible to form a suitable inorganic layer in which there are no splits or cracks on an entire surface of the film. Accordingly, a gas barrier film which sufficiently exhibits a high gas barrier property of the inorganic layer is obtained.
In addition, the laminated structure of the organic layer as the base and the inorganic layer is formed by being repeated, and thus it is possible to obtain a higher gas barrier property. Furthermore, the organic layer for protecting the inorganic layer may be formed on the inorganic layer.
By using the gas barrier film in which the organic layer as the base and the inorganic layer are laminated in the organic EL device, it is possible to confer a high gas barrier property thereon.
However, in the organic EL device, it is difficult to use a gas barrier film in which a low retardation film is formed as a support body, and an organic layer as a base and an inorganic layer are formed.
As described above, when the plastic film is used on the light extraction side of the organic EL device, the low retardation film formed of a polycarbonate or a cyclo-olefin polymer is required to be used.
In general, the low retardation film is manufactured by solution film forming. As is well known, solution film forming is a method of manufacturing a plastic film by dissolving plastic (a resin material) to be a film in an organic solvent, by flow-casting the dissolved plastic on a flat plate or a drum, and by drying the cast.
The plastic film manufactured by the solution film forming is not molded by extrusion, stretching, or the like. For this reason, the plastic film is non-oriented, and does not have birefringence. Accordingly, it is possible to manufacture the low retardation film (a plastic film of low retardation) according to the solution film forming.
On the other hand, in the gas barrier film which is formed by laminating the organic layer to be a base and the inorganic layer, the organic layer is generally formed by a coating method.
As is well known, an organic layer may be formed by a coating method in which a coating material formed by dissolving a monomer (an oligomer), a polymerization initiator, and the like to be an organic layer in an organic solvent is prepared, the coating material is coated on a formed portion and is dried, and the monomer is polymerized by ultraviolet irradiation, electron beam irradiation, or the like.
That is, when the gas barrier film having the laminated structure of the organic layer as the base and the inorganic layer is manufactured by using the low retardation film as the support body, the organic solvent contained in the coating material for forming the organic layer as the base dissolves the low retardation film which is manufactured by solution film forming. In addition, the low retardation film is not limited to the low retardation film formed by solution film forming, but is likely to be dissolved by the organic solvent due to a chemical structure thereof.
As a result thereof, a retardation value of the low retardation film or a film which is designed to have a predetermined retardation value or to be a phase difference film is considerably changed. Furthermore, considerable degradation of various optical characteristics such as a decrease in light transmissivity of the low retardation film due to dissolution, and an increase in haze is caused.
For this reason, by using the gas barrier film in which the low retardation film is formed as the support body, and the organic layer as the base and the inorganic layer are laminated in the organic EL device, it is possible to confer a high gas barrier property thereon, but optical characteristics of an essential organic EL device are degraded.
Such a problem may be solved by selecting an organic solvent used for a coating material for forming an organic layer.
However, an organic solvent which does not dissolve the low retardation film is generally an organic solvent having a high boiling point, or an organic solvent having a high molecular weight. It is difficult for drying of the coating material using such an organic solvent to be controlled, and controllability of a dried film such as leveling is degraded.
For this reason, when an organic layer is formed by the coating material using such an organic solvent, a covering property for the surface of the support body with respect to the organic layer or surface flatness of the organic layer becomes insufficient. As a result thereof, it is not possible to form a suitable inorganic layer on the organic layer which is the base, and thus a sufficient gas barrier property may not be obtained.
On the other hand, a gas barrier film formed by laminating an inorganic layer and an organic layer in which an inorganic layer is formed on the surface of the plastic film which is the support body, the organic layer is formed thereon, and an inorganic layer is further formed thereon is also known.
For example, a gas barrier film having a configuration in which an inorganic layer formed of silicon, aluminum oxide, nitride, or the like is formed on a surface of a plastic film, an organic layer formed of a polyacrylate, a polymethacrylate, or the like is formed thereon, and an inorganic layer similar to the organic layer described above is formed, and 99.5 mass % or more of a compound forming the organic layer is solid at 25° C. is disclosed in JP2007-30387A.
Since the gas barrier film disclosed in JP2007-30387A has such a configuration, and thus has high strength, when the gas barrier film is used as a substrate of an organic EL device, it is possible to effectively suppress dark spots.
In addition, a gas barrier film in which a silicon oxynitride layer is formed on a surface of a plastic film, an organic intermediate layer formed of an acrylate compound or the like is formed thereon, and a silicon oxynitride layer is formed thereon is disclosed in JP2007-253590A.
Since the gas barrier film disclosed in JP2007-253590A has such a configuration, a gas barrier film having a high gas barrier property is obtained at high productivity by continuous film forming.